This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The acid certainly exerts some control over exalted cerebral function, whether by acting through the circulation or otherwise. Vertigo, especially, if dependent on gastric derangement, may be relieved by it. Dr. McLeod has furnished evidence of its calmative power in acute mania and acute melancholia, recording forty cases, in most of which the relief given to violent excitement was marked and rapid; about 5 min. of Scheele's acid was the usual dose, or 3 min. injected under the skin (Medical Times, i., 1862).
In Delirium Tremens, Dr. Dow has seen it serviceable (British Medical Journal, i., 1873), and Dr. Maudsley recommends its combination with digitalis (Practitioner, January, 1869, vol. ix.).
Acidum hydrocyanicum dilutum (contains 2 per cent. of anhydrous acid): dose, 2 to 8 min. Vapor acidi hydrocyanici (inhalation) is prepared with 10 to 15 min. in 1 fl. dr. of cold water. "Mix in a suitable apparatus, and let the vapor that arises be inhaled." Lotio: 2 dr. to 1/2 oz. in 1/2 pint of rose water; it should not be applied to an abraded skin. Anhydrous prussic acid being one of the most active and rapid poisons known, should never be prescribed; neither should Scheele's prussic acid, which contains 4 per cent. of anhydrous acid.
[Preparation, U.S.P. - Acidum hydrocyanicum dilutum, contains 2 per cent. of anhydrous acid.]